The article acquaints the reader with the peculiarities of the formation of the territory of the early medieval empire of Ukraine-Rus, its marking, legal and ideological support for its centralization, and the divisiveness that became one of the reasons for its disintegration. The authors come to the conclusion that the structuring of state power in Ukraine-Rus was based on the transformations of Prince Volodymyr the Great, who carried out administrative, military, land, financial, religious, and judicial reforms. The reforms were based on the territorial principle of political consolidation of the subjects that formed Ukraine-Rus, the ancestral principle of ownership and protection of its territories by representatives of the Rurik ruling family, the principle of establishing a state-building ideology to ensure its integrity, and the dynastic principle of strengthening at the international level. In the political dimension, the reform was aimed at overcoming the separatism of the local regional, mainly tribal elite and the ruling princely clans of individual lands-principalities. The prince liquidated the tribal principalities (lands). In this way, the influence of the powerful boyar clans, consisting of the descendants of the tribal aristocracy within the lands, was significantly limited. The entire territory of the country was divided into eight volosts, they were headed by Volodymyr’s sons, and in the most important cities the boyars (officials) appointed by him were established. In order to ensure the ideological unity of the empire, Volodymyr carried out a religious reform – the introduction of Christianity as the state religion. The legal consolidation of the religious reform was provided by the Church Statute of Prince Volodymyr. However, Christianity as a state-building ideology never became the value system that could mobilize society, especially the representatives of the Rurik ruling dynasty, to fulfill the internal tasks of state-building. The formation of the state was brought to a logical conclusion by Grand Duke Yaroslav the Wise of Kyiv, who finally broke local separatism and stabilized the state territory and its borders. However, he did not manage to overcome the tendency to infighting in the middle of the ruling family of the Rurikovichs, which ended in a particular fragmentation, disputes over the Kyiv throne. The final point in the development of Ukraine-Rus was put by the Mongol-Tatar invasion on the land of Ukraine. Kyiv as the political center of the empire declined. With its loss of economic and political importance, the geopolitical role of the Western Russian lands increased. The Galician-Volyn state took over the best traditions of its predecessor, supplementing them with novels borrowed from the state-building experience of medieval European countries.